Bumpy Fuel Table

Forum for general discussions on engine tuning, not specific to a particular motec ECU

Bumpy Fuel Table

Postby Vlad on Wed Sep 29, 2021 4:30 pm

Hi guys, si it's been a long time since i want to debate this with somebody else. I've tuned numerous NA high performance engines. Last night for example, i've finished this Renault, engine is a regular NA, no valve timing control, no nothing, just ITB's, cams, high CR, etc. The fuel table, needs to look like this (Picture) in order for me to have a steady'ish Lambda...Can an engine really induce air this unevenly? 252nm at 5600rpm and 278hp at 8100.... Again, with the table looking like this, the Lambda is quite close to the lambda target. Also, this happened on other engines too, aspirated To be honest, i've mapped a Sodeomo F4R, peaking 280hp and the table was way smoother than a same engine, almost same 280hp, but homemade... I have a degree in mechanical engineering, but still strugle to understand what the hell is going on..... Cheers

Regards, Vlad.
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Vlad Pescaru
JPR Engineering, MoTeC Authorised Dealer
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Re: Bumpy Fuel Table

Postby SDean on Wed Sep 29, 2021 4:44 pm

Hi Vlad,

I have seen plenty of ITB maps that look like that, it's actually smoother than a number that I have seen. The peaks and valleys are caused by the different airflow characteristics at different inlet flow velocities, in some areas the reversion wave will be arriving back at the valve at the same time that it is opening, thus increasing the Volumetric Efficiency of the engine, requiring more fuel to maintain the requested Lambda Aim. In other places this reversion wave will work against you, and lower the VE, lowering the fuel requirement to maintain the Lambda aim.

Here are some other maps.

86.JPG
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MINI.JPG
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STi.JPG
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Stephen Dean
MoTeC Research Centre Melbourne, Australia
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Re: Bumpy Fuel Table

Postby SprinterTRD on Wed Sep 29, 2021 4:54 pm

Seen this plenty of times.
This is where inlet tract length and diameters, and exhaust design & tuning comes into play!
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Re: Bumpy Fuel Table

Postby Sean on Sun Oct 31, 2021 2:35 pm

6.7 litre V8 with ITB, map sensor measuring airbox pressure. Where that canyon is it can't hold a stable rpm on the dyno, you can come down from the high rpm, or up from the low, it reaches a point where it's unstable.

map1.jpg
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